[Vulkan] Honor downcast_64_bit=False in the partitioner - #23248

Draft

mergennachin wants to merge 6 commits into

gh/mergennachin/31/headfrom

gh/mergennachin/32/head

Commits on Sep 29, 2026

[INITIAL] Recreate the Vulkan transformer and conformance stack with ghstack
mergennachin
committed
836dc54

Commits on Oct 3, 2026

[UPDATE] Rebase remaining Vulkan stack onto main after parts 1–3 landed
mergennachin
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b066808
[UPDATE] Cover exact FP16 halfway rounding in texture reductions
mergennachin
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6f39097
[UPDATE] Match arg-reduction partitioning to the buffer-only last-dimension kernel; rebase after PR 23243 landed
mergennachin
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83d3ac3
[UPDATE] Add exact FP16 zero/subnormal and overflow-threshold coverage
mergennachin
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fb9b582
[UPDATE] Exercise int32 reduction shaders directly beyond the removed clamp
mergennachin
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6942500